Combine harvesters generally have a pickup reel with a cutting table, which can be twice as wide as the width of the harvester. This means that during harvest of straw fodder plants, the chaff after the treshing will be deposited on the field in a rather narrow string, which mainly corresponds to the width of the cleaning device. It nowadays is usual that the straw after treshing is cut and spread over an area mainly corresponding to the width of the cutting table, in order to allow it to be plowed into the soil. The field therefore will have row-formed areas, where the content of disintegrated straw and chaff is bigger than in adjacent areas, which almost entirely lack an admixture of chaff. This uneven distribution results in different growth conditions due to the fact that the growth is hampered in the areas where the soil contains too much disintegrated, but non-mouldered straw and chaff.
There are known treshing machines for treshing cut straw fodder plants, where the chaff from the cleaning device is supplied to a rotary chopper or a straw shredder. The purpose of this mixing of straw and chaff is to improve the nutritional value, in the case where straw is used as fodder. For this reason the rotary chopper outlet is usually equipped with a pressing device, which crushes the straw and the ears.
It was proven that the known technique is impossible to use, as the modern rotary chopper creates a positive pressure about the rotor, which pressure is so big so that the chaff is blown away, causing a blocking of the straw inlet. It also has been tried to feed the chaff tangentially in through a separate opening in the rotary chopper or the straw shredder, but the same problem also occurs in this case, i.e. the positive pressure from the rotor prevents the chaff from entering the rotary chopper. According to another suggestion (British patent No. 4220 from 1893) the chaff is transported by means of a particular blower via a conduit system to a position above the inlet of the rotary chopper. In order to transport the quantities of chaff concerned a rather big positive pressure in the blower is required, which means that an air cushion is created above the rotary chopper, which may cause the straw feed to be blocked.